v2.2.0

enable 64-bit processing (2GiB+ file sizes) within constraints that no single sub-graph can exceed 2GiB; this is assisted by…

new IsGroup property on [ProtoContract(...)] that indicates that a type should always be treated as a group (rather than having to specify “group” per-member); groups do not require length-prefix or buffering, so are trivially usable in huge files